Chronic noncancer pain, defined as pain lasting three months or longer, is prevalent worldwide. While opioid treatment is an option for relieving pain, concerns have been raised about its long-term efficacy and safety. Noble and colleagues reviewed 26 studies involving 4,893 participants with chronic noncancer pain who'd been taking an opioid for at least six months.

The studies examined different types of pain: back, osteoarthritis, unspecified, neuropathic, osteoporotic vertebral fracture, and trigeminal neuralgia. The dose, type, and route of opioid administration varied among the studies. Types of opioids administered included morphine, oxycodone, oxymorphone, dihydrocodeine, and tramadol, among others. Most were administered orally (12 studies) or through an implantable infusion pump (10 studies), while five studies involved transdermal administration.

Consolidated study results showed clinically significant reductions in pain in patients who continued opioids long term, but many discontinued opioid treatment either because it didn't provide pain relief or because of adverse events. The most common adverse events were gastrointestinal effects, headache, and urinary complications. Serious adverse events, such as addiction, were rare, with signs of addiction observed in only 0.27% of participants. Results of an analysis of the effects of opioid use on quality of life were inconclusive.

The authors noted that all studies excluded participants with a history of addictive or abusive behavior, thus limiting the extent to which the results can be generalized. They concluded that further research is needed to identify those patients for whom long-term opioid treatment would be most effective.